Field of the Invention
The present invention relates to a back protective sheet for a solar cell module and a solar cell module.
Background Art
A solar cell is an environmental load-reducing power generation system that releases no carbon dioxide in power generation, and has become greatly popularized recently.
A solar cell module generally has a structure in which a photovoltaic cell is sandwiched between a front glass on the side on which sunlight is incident, and a back protective sheet for a solar cell module (a so-called back sheet) arranged on the side opposite (back side) to the side on which sunlight is incident, and the space between the front glass and the photovoltaic cell and the space between the photovoltaic cell and the back sheet each are sealed up, respectively, with an EVA (ethylene-vinyl acetate) resin or the like.
The back sheet has a function to prevent from penetration of moisture from the back surface of the solar cell module, for which glass, fluororesin, or the like has been heretofore used. Recently, however, a polyester has become used from the viewpoint of the cost. Further, as the front substrate, a glass substrate is generally used from the viewpoint that its light transmittance is high and a relatively high strength can be maintained. However, there is also a recent approach to use a back protective sheet in place of the glass substrate or the like.
A back protective sheet for a solar cell module as such a protective sheet for a solar cell may be provided with a functional layer on a polymer support in accordance with the desired characteristics in some cases. For example, a back sheet is used on the back side of a solar cell and is desired to have durability (hydrolysis resistance and electric insulation), adhesiveness of an Si cell to a sealing material, reflectance, and the like. As a back sheet provided with such a functional layer, Patent References 1 to 4 propose a coating type back sheet, and Patent References 5 to 7 propose a laminate type back sheet.
The coating type back sheet is prepared by applying a solution prepared by dissolving functional materials in an organic solvent or water, onto a support sheet of a polyester or the like at room temperature or at a suitable high temperature, thereby affording a structure in which the support and the functional layer are arranged to be in contact with each other and an adhesive or the like is not interposed therebetween. An advantage of the coating type back sheet is that the production cost can be reduced, as compared with the laminate type back sheet as described in Patent References 5 to 7.
On the other hand, there is the case where since an adhesive is not used and a functional layer is provided by coating, the adhesion between the support sheet and the functional layer is deteriorated. In particular, it has now become investigated to install a solar cell module in a high-temperature high-humidity environment in which the back protective sheet for a solar cell module itself is easily deformed, and operate solar cell module for a long time from the viewpoints of improvement in power generation efficiency and size in recent years, and particularly, it is desired to maintain the adhesion between the layers of the back sheets over time in a high-temperature high-humidity environment.